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[en] The characteristics of a capacitively coupled CHF3 plasma driven by dual-frequency sources (41 MHz/2 MHz) are experimentally investigated by using optical emission spectroscopy technique. The dependences of relative densities of F and H, the ratio of F/CF2, and the excitation temperature, as well as neutral gas rotational temperature on the low or high frequency (LF or HF) power, have been analyzed. It is found that the increment rate of the gas dissociation rate, the ratio of F/CF2, the excitation temperature. and the neutral gas temperature with increasing LF power are larger than that of HF power. The relative densities of F and H, the ratio of F/CF2, and the excitation temperature decrease while the neutral gas temperature increases with increasing gas pressure.
[en] A global or zero-dimensional model for C4F8 plasmas is formulated by coupling gas phase and wall surface reaction kinetics. A set of surface reactions implements experimental findings and quantifies the effect of the fluorocarbon film formed on the reactor walls on the densities of species in the gas phase. The model allows the calculation of the pressure change after the ignition of the discharge and the effective sticking (surface loss) coefficients of the neutral species on the wall surface. The model is validated by comparison with experimental measurements, i.e. pressure rise and densities of F atoms, CF2 and CF radicals, in an inductively coupled plasma reactor. It is predicted that C4F8 is vastly dissociated and CF4 becomes the dominant species even at low power conditions. A net production of CF3 radical and a net consumption of CF2 radical at the reactor walls are predicted. A study on the contribution of each reaction to the production and consumption of the species shows that at least one surface reaction is among the major sinks or sources of CF4, CFx radicals and F.
[en] Due to high sensitivity to process parameters, plasma processes should be tightly controlled. For plasma control, a predictive model was constructed using a neural network and optical emission spectroscopy (OES). Principal component analysis (PCA) was used to reduce OES dimensionality. This approach was applied to an oxide plasma etching conducted in a CHF3/CF4 magnetically enhanced reactive ion plasma. The etch process was systematically characterized by means of a statistical experimental design. Three etch outputs (etch rate, profile angle, and etch rate nonuniformity) were modeled using three different approaches, including conventional, OES, and PCA-OES models. For all etch outputs, OES models demonstrated improved predictions over the conventional or PCA-OES models. Compared to conventional models, OES models yielded an improvement of more than 25% in modeling profile angle and etch rate nonuniformtiy. More than 40% improvement over PCA-OES model was achieved in modeling etch rate and profile angle. These results demonstrate that nonreduced in situ data are more beneficial than reduced one in constructing plasma control model
[en] A Si etching process has been investigated with reactive neutral beams (NBs) extracted using a low acceleration voltage of less than 100 V from CF4 and Ar mixed plasmas. The etched Si profile shows that the etching process is predominantly anisotropic. The reactive NB has a constant Si etching rate in the acceleration voltage range from 20 V to 80 V. It is considered that low-energy NBs can trigger Si etching because F radicals adsorb onto the Si surface and weaken Si–Si bonds. The etching rate per unit beam flux is 33 times higher than that with Ar NB. These results show that the low-energy reactive NB is useful for damage-free high speed Si etching
[en] Results: of the investigation of time-amplitude characteristics of thin-walled drift tubes (straws) of different diameters for gas mixtures ArCO2 with CF4 and O2 additives are described. An essential reduction of the sensitivity time of the straw for CF4 additive is shown, especially with increase the straw diameter. O2 additive influences the time parameters of the straw insignificantly. CF4 or O2 additives with the so-called cleaning properties are of interest for optimization of parameters of detectors with small sensitivity time under the condition of high loadings.
[en] Photoion images from photoionization of CF4 with an isotropic geometry have been measured in the photon energy range of 17-60 eV. Fragment ion emissions below 40 eV are found to be anisotropic with respect to the electric vector of the linearly polarized light. This observation directly implies that the T d symmetry is broken on the dissociative photoionization process. The excited states associated with the transitions to the unoccupied orbitals are subject to symmetry lowering, which promotes the anisotropic fragment emissions from the highly-symmetrical molecule
[en] In CF4 based discharges admixed with oxygen the density of CF2 radicals decreases with an increase in the oxygen flow at a fixed CF4 flow and pressure. This decrease is attributed to the increased reaction of CF2 radicals and O atoms in the bulk plasma and to the O2 dilution effect. By taking into account these two factors the behavior of the densities of CF2 radicals, F and O atoms in CF4/O2 discharges was theoretically investigated in terms of oxygen flow using a simple plasma chemistry model. The data provided by Buchmann et al. [J. Appl. Phys. 67 (1990) 3635] were interpreted based on the proposed model, and the validity of the model was discussed
[en] The kinetics of the production and loss of CF2 radicals in a tetrafluorinemethane plasma in a dc discharge is studied. The absolute CF2 concentration is measured by a differential-absorption technique in the UV band of CF2 on the 1A1(000)→1B1(060) and 1A1(000)→1B1(030) transitions, and the electric field on the axis of the positive column of the discharge is measured by a two-probe technique. All measurements are carried out in the pressure range from 0.2 to 1 torr at discharge currents from 5 to 40 mA. Based on the experimental data, the rate constant of electron-impact dissociation of CF4 molecules leading to the formation of CF2 radicals is determined as a function of the reduced electric field. The cross section for the process in question is inferred from a comparison of the published data on the dissociation cross sections for CF4 molecules with the results obtained in this study
[en] A two-dimensional hybrid model is used to study the two-dimensional characters of the plasma parameter such as the ion flux, the ion energy and angular distributions in radial and axial directions. It shows that the electric field and the sheath character at the center of the electrode are different from those at the area between the electrode and the side wall. At the area between the electrode and the side wall, the influence of the electrode is relatively small, and the sheath structure is determined by the ambipolar diffusion. Therefore, the axial electric field is small, the radial electric field is relatively stronger, and the sheath near the side wall is much thinner than that in the center of the RF electrode. The ion flux and the ion energy distributions on the electrode remain the same at the center area of the discharge chamber, however, the electric field in axial direction decreases between the side wall and the edge of electrode, which leads to a decrease of the ion flux in this region. The ion angular distributions also have little change at the center area of the discharge chamber. However, the radial electric field becomes stronger than the axial field between the side wall of the chamber and the edge of the electrode. This makes the ions in that area strike the lower electrode with a much larger angle. (authors)